SageMaker’s new training-session APIs let developers define post-training algorithms while AWS manages GPU execution, recovery and checkpointing.
Amazon Web Services made training-session APIs generally available in Amazon SageMaker AI on October 22. The feature gives developers more control over how they customize a model while AWS manages the GPU-backed infrastructure, expanding the service’s serverless model-customization options.
Developers can write and coordinate their own post-training loops rather than selecting only a preset recipe. The APIs expose operations such as sampling model responses, calculating gradients and applying optimization steps. This supports workflows including supervised fine-tuning, preference optimization and reinforcement learning, as well as custom loss functions or reward signals.
The division of work is intended to reduce infrastructure management, not remove the need to design and evaluate training. Customers supply the data, training logic and reward function; SageMaker handles GPU allocation, distributed execution, fault recovery and checkpoint storage. AWS says usage is billed by processed tokens, with billing paused while customer code scores a batch outside the GPU-backed operations.
AWS listed gpt-oss-20b, gemma-4-31B-it, Qwen3.6-27B and Qwen3.8-27B among the supported models at launch. The service was announced for US East (N. Virginia), US West (Oregon) and Asia Pacific (Mumbai); model availability can vary by region. AWS also released a cookbook with example supervised fine-tuning and reinforcement-learning recipes.
The release targets teams that need custom training procedures for specialized models or multi-step agents but do not want to operate GPU clusters themselves. AWS cited early use cases including healthcare claim-denial triage and tuning a model for multi-turn tool use with an Amazon Neptune knowledge graph. Those examples illustrate possible applications, but the announcement did not provide comparative figures establishing improvements in accuracy, cost or deployment speed.
